SUMMARY: The BAC Recombineering and Transgenic Targeting Core (BRTT) will generate, characterize and distribute specialized transgenic lines requested by the NIDA PSO Center for Molecular and Epigenetic Research of Cell Types Mediating Addictive Behaviors. The BRTT core will be in charge of the following subprojects/tasks: 1) BAC modification of Cre-recombinase and TRAP vectors, 2) Generation of BAC transgenic mice, 3) Histological confirmation of accurate transgene expression, and 4) Archive and distribution of BAC transgenic mice